Biventricular strain and strain rate impairment shortly after surgical repair of tetralogy of Fallot in children: A case‐control study

Abstract Background Early biventricular dysfunction in repaired tetralogy of Fallot (TOF) children may lead to poor clinical outcomes. We aimed to assess biventricular function in TOF children before and after surgery by speckle tracking echocardiography (STE) and compare them with the controls. Methods Twenty repaired TOF children and 20 normal children as controls were assessed by STE. Tricuspid annular plane systolic excursion (TAPSE), left ventricular ejection fraction (LVEF), biventricular strain, and strain rate were compared before and after surgery and between TOF children and controls. Results Postoperative LVEF (p = 0.001), strain (p = 0.001), and strain rate (p = 0.001) for left ventricle improved significantly compared to preoperative phase. However, postoperative left ventricular strain (p = 0.05) and strain rate (p = 0.01) in TOF children were significantly impaired compared to controls. Postoperative LVEF was correlated inversely with postoperative strain rate (r = −0.40, p = 0.04). Postoperative TAPSE (p = 0.001), strain (p = 0.001), and strain rate (p = 0.001) for right ventricle significantly worsened when compared with the preoperative phase. Moreover, postoperative TAPSE (p = 0.001), strain (p = 0.001), and strain rate (p = 0.01) were significantly impaired compared to controls. Postoperative right ventricular strain rate was correlated significantly with the weight of children (r = 0.48, p = 0.02), and postoperative left ventricular strain showed significant correlations with aortic clamp time (r = 0.44, p = 0.04) and with ICU stay (r = −0.46, p = 0.04). Conclusion Despite normal LVEF, TOF children exhibit impaired left ventricular strain and strain rate after surgery. TAPSE, strain, and strain rate for the right ventricle worsen after surgical repair. STE‐driven strain can be used to detect early ventricular dysfunction and the associated prognostic implications.


| INTRODUCTION
Tetralogy of Fallot (TOF) is among the most common type of congenital cardiac anomalies typified by ventricular septal defects, overriding of the aorta, pulmonary stenosis, and hypertrophy of the right ventricle. 1,2 Although surgical correction of TOF is often required to relieve the cyanotic condition during the newborn period, it can increase the risk of morbidity and mortality, especially in highrisk patients with small size, genetic disorders, and other comorbidities. [3][4][5] Speckle tracking echocardiography (STE) technique was introduced as a scientific approach for evaluating global and regional myocardial function and has been broadly validated in various clinical settings such as evaluating ventricular function. 6,7 Advantages of STE include assessing radial and longitudinal myocardial deformation independence of the insonation angle and overcoming the requirement of manual tracking of myocardial wall segments during the cardiac circle. 8,9 In contrast with traditional echocardiography, STE provides a meticulous analysis of global and regional myocardial function. 10 Moreover, evaluation of cardiac function by traditional echocardiography using ejection fraction has shown limitations in the diagnosis of early stages of right and left ventricular systolic dysfunction. 11 It has been demonstrated that STE is a promising innovative approach in the early diagnosis of deteriorated right and left ventricular systolic function by measuring longitudinal strain and strain rate. 12 Despite the potential benefits of STE, there are limited data on assessing early changes in biventricular function in pediatric with congenital cardiac anomalies, particularly surgically repaired TOF children. 13 We conducted this study to determine early longitudinal changes in right and left ventricular function through measurement of strain and strain rate by STE in repaired TOF children.

| Study design and ethics
This case-control study was carried out on TOF children admitted to our center and underwent surgical repair. , and other cardiac comorbidities (n = 2), and Down syndrome (n = 1). Twenty age-matched children with innocent heart murmurs who were referred to the pediatric cardiology clinic for consultation were selected as a control group.

| Surgical approaches
All surgical approaches were done under general anesthesia and the establishment of cardiopulmonary bypass. As we described previously, following the relief of right ventricular outflow tract obstruction by a transannular patch, the anterior portion of the ventricular septal defect was closed using a polytetrafluoroethylene patch through a short atriotomy and minimal retraction of the tricuspid valve. Afterward, the inferior part of the ventricular septal defect was closed via a limited ventriculotomy and minimal manipulation of the right ventricle. 3 15 Accordingly, worsening in ventricular function was defined as a decrease in the magnitude of strain over time and an increase in the magnitude of strain was considered as an improvement in ventricular function.

| Statistical analysis
All statistical analyses were performed using the SPSS 24.0 software (SPSS). Categorical variables were represented as frequency (%) and continuous variables as mean ± standard deviation. Kolmogorov-Smirnov test was applied to control whether data had a normal distribution or not. Categorical data were analyzed by χ 2 test and Fisher's exact test where appropriate. Paired t-test was applied to compare pre-and postoperative variables and an unpaired t-test was applied to compare continuous data between two groups of study.
Correlations between LVEF and TAPSE with strain and strain rate for right and left ventricles were calculated as Pearson's correlation coefficients. p Value was considered statistically significant when it was less than 0.05.

| Demographic data and patient characteristics
Twenty TOF children and 20 controls were screened and enrolled in this study. Comparisons between TOF children and controls are summarized in Table 1. TOF children consisted of 12 males and 8 females, whereas the controls consisted of 13 males and 7 females. STE data of one male TOF child was excluded from the final analysis because he experienced postoperative complete heart block and received a permanent pacemaker. There were no statistically significant differences in age, weight, body surface area, systolic blood pressure, and diastolic blood pressure between the two groups of study. Preoperative O 2 saturation was significantly lower in TOF children than controls (89.80 ± 2.09% vs. 95.70 ± 1.95%, p = 0.001).

| Operative and postoperative outcomes
In the TOF children undergoing a total correction, the mean duration of cardiopulmonary bypass and aortic cross-clamp times were 128 ± 32 and 91.20 ± 20.6 min, respectively. Before surgery, the mean oxygen saturation was 89.80 ± 2.09% which increased significantly to 95.20 ± 1.36% after surgical repairer (p = 0.001). Intraoperative and postoperative outcomes are summarized in Table 2.

| Left ventricular performance
The LVEF, strain, and strain rate for the TOF children and controls are shown in Figure    rate are close to the controls. 22 Weidemann et al. report has shown abnormal function in regional biventricular systolic myocardial function in asymptomatic repaired TOF children that are related to irregular electrical depolarization in the right ventricle. 23 Furthermore, a recent study in the assessment of biventricular function

CONFLICTS OF INTEREST
The authors declare no conflicts of interest.

DATA AVAILABILITY STATEMENT
Related data of this project are available on request.

TRANSPARENCY STATEMENT
The lead author (manuscript guarantor) affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.